System

By default, ExceptClsProc is defined internally to point to a function that handles exceptions on your behalf. It returns the exception class. If you override ExceptClsProc to point to your function, that function will be called when an exception occurs in a try-except block. It will be passed an updateable TExceptionRecord value that describes the exception.  

Internally, the class returned is used to determine which exception handler to use before ExceptObjProc is called to create the exception instance. 

ExceptObjProc 

TExceptionRecord